Coating agent based on polymers containing carboxyl groups and crosslinking agents containing epoxide groups, processes for the preparation of the coating agent and its use

Abstract

PCT No. PCT/EP90/01173 Sec. 371 Date Jan. 24, 1992 Sec. 102(e) Date Jan. 24, 1992 PCT Filed Jul. 18, 1990 PCT Pub. No. WO91/02036 PCT Pub. Date Feb. 21, 1991.The present invention relates to coating agents containing A) one or more polymers containing carboxyl groups and having a number-average molecular weight of 500 to 8,000 and an acid number of 15 to 200 mg of KOH/g as the essential binder component and B) one or more compounds containing epoxide groups as crosslinking agents, wherein the compound B containing epoxide groups is a copolymer containing epoxide groups, has a number-average molecular weight Mn of 300 to 5,000, preferably 500 to 3,500, and a heterogeneity (Mw/Mn), measured by gel permeation chromatography, of <=3, preferably of <=2, and has been prepared by continuous bulk polymerization at temperatures between 130 degrees and 350 degrees C. and pressures above 1 bar. The invention also relates to processes for the preparation of the coating agent and the use of the coating agents in automobile refinishing.

We claim: 
     
       1. A coating agent comprising: A) a polymer selected from the group consisting of a copolymer containing carboxyl groups, a polyester containing carboxyl groups and mixtures thereof, said polymer having a number-average molecular weight M n  of 500 to 8,000 and an acid number of 15 to 200 mg of KOH/g as the essential binder component; and   B) at least one compound containing epoxide groups as crosslinking agents; wherein the compound B containing epoxide groups is a copolymer containing epoxide groups, has a number-average molecular weight M n  of 300 to 5,000 and a heterogeneity (M w  /M n ), measured by gel permeation chromatography, of ≦3 and has been prepared by continuous bulk polymerization at temperatures between 130° and 350° C. and pressures above 1 bar of a) 10 to 60% by weight of at least one vinylaromatic hydrocarbon;   b) 10 to 50% by weight of at least one ethylenically unsaturated monomer containing at least one epoxide group per molecule; and   c) 5 to 80% by weight of other ethylenically unsaturated copolymerizable monomers; the sum of the weight contents of components (a) to (c) in each case being 100% by weight.     
     
     
       2. A process for the preparation of a coating agent comprising: A) a polymer selected from the group consisting of a copolymer containing carboxyl groups, a polyester containing carboxyl groups and mixtures thereof, said polymer having a number-average molecular weight M n  of 500 to 8,000 and an acid number of 15 to 200 mg of KOH/g as the essential binder component and   B) one or more compounds containing epoxide groups as the crosslinking agent, which comprises: mixing the binder component A and the crosslinking agent B only shortly before application of the coating agent, wherein the compound B containing epoxide groups is a copolymer which contains epoxide groups, has a number-average molecular weight M n  of 300 to 5,000, and a heterogeneity (M w  /M n ), measured by gel permeation chromatography, of ≦3, and has been prepared by continuous bulk polymerization at temperatures between 130° and 350° C. and pressures above 1 bar of a) 10 to 60% by weight of one or more vinylaromatic hydrocarbons,   b) 10 to 50% by weight of one or more ethylenically unsaturated monomers containing at least one epoxide group per molecule and   c) 5 to 80% by weight of other ethylenically unsaturaged copolymerizable monomers,      the sum of the weight contents of components (a) to (c) in each case being 100% by weight.     
     
     
       3. A coating agent as claimed in claim 1, wherein the compound B has a number-average molecular weight M n  of 500 to 3,500. 
     
     
       4. A coating agent as claimed in claim 1, wherein the compound B has a heterogeneity (M w  /M n ), measured by gel permeation chromatographly, of ≦2. 
     
     
       5. A coating agent as claimed in claim 1, wherein the copolymer B containing epoxide groups has been prepared by bulk polymerization of a) 15 to 50% by weight, of one or more vinylaromatic hydrocarbons,   b) 15 to 50% by weight of one or more ethylenically unsaturated monomers containing at least one epoxide group per molecule and   c) 20 to 50% by weight, of other ethylenically unsaturated copolymerizable monomers, the sum of the weight contents of components (a) to (c) in each case being 100% by weight.     
     
     
       6. A coating agent as claimed in claim 1, wherein the copolymer B containing epoxide groups has been prepared using glycidyl methacrylate as one of the ethylenically unsaturated monomers. 
     
     
       7. A coating agent as claimed in claim 1, wherein the copolymer B containing epoxide groups has been prepared using alkyl esters selected from the group consisting of acrylic acid, methacrylic acid or mixtures thereof as one of the ethylenically unsaturated monomers. 
     
     
       8. A coating agent as claimed in claim 1, wherein the copolymer B containing epoxide groups has an epoxide equivalent weight of 150 to 2,000. 
     
     
       9. A coating agent as claimed in claim 8, wherein the copolymer B containing epoxide groups has an epoxide equivalent weight of 500 to 1,000. 
     
     
       10. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A have an acid number of 30 to 120 mg of KOH/g. 
     
     
       11. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A have an amine number of 0 to 50 mg of KOH/g. 
     
     
       12. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A have an amine number of 10 to 40 mg of KOH/g. 
     
     
       13. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A have been prepared by a procedure in which a polymer containing hydroxyl groups and having an OH number of 30 to 200 mg of KOH/g has first been prepared and has then been reacted with carboxylic acid anhydrides to give the corresponding polymers containing carboxyl groups. 
     
     
       14. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A have likewise been prepared by continuous bulk polymerization at temperatures between 130° and 350° C. and pressures above 1 bar. 
     
     
       15. A coating agent as claimed in claim 1, wherein the polymers which contain carboxyl groups and are employed as the binders A are copolymers prepared by free radical solution polymerization. 
     
     
       16. A coating agent as claimed in claim 1, wherein the coating agent contains: A) 10 to 70% by weight, based on the total weight of the coating agent, of binder A containing carboxyl groups;   B) 10 to 50% by weight, based on the total weight of the coating agent, of crosslinking agent B containing epoxide groups;   C) 20 to 50% by weight, based on the total weight of the coating agent, of one or more organic solvents; and   D) 0 to 60% by weight, based on the total weight of the coating agent, of pigments and fillers; and   E) 0 to 10% by weight, based on the total weight of the coating agent, of customary auxiliaries and additives.   
     
     
       17. A process for automobile repair refinishing, wherein a coating agent as claimed in claim 1 is applied. 
     
     
       18. A process for automobile series painting, where a coating agent as claimed in claim 17 is applied.